By B Monakov; Z M Sabirov; N N Sigaeva
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Extra resources for Active sites of polymerization: multiplicity: stereospecific and kinetic heterogeneity
Therefore, the rate constant of chain propagation does not practically change. Moreover, none of sufficient changes in the microstructure of synthesized polyisoprene were observed. 2). 2. HETEROGENEITY OF ACTIVE SITES IN IONICCOORDINATE POLYMERIZATION OF DIENES In 1954, catalytic systems for ionic-coordinate polymerization of unsaturated compounds were discovered by Carl Ziegler, and then polymerization of a-olefins and dienes with them was systematically studied by Julio Natta. These two events have provided for both synthesis of polymers, which may not be produced on other catalysts (for example, highmolecular propylene polymers and some higher a-olefins) and formation of macromolecules with highly regulated chain structure (1,4-cis- and 1,4-transpolydienes, iso- and syndiotactic polymers).
The Monte-Carlo method was applied  to modeling of the size change, spatial distribution of catalyst particles and adsorption of multiatomic molecules on them influence on distribution of the catalyst active sites by reactivity. 1 shows investigation results on ethylene polymerization in toluene on MgH2/TiCl4-AI(C2Hs)3 catalytic system . B. N. N. Urazbaev sites after catalyst contact with ethylene during 60 minutes was determined using 14CO probes injected to polyethylene. It is obvious that the catalytk system shows the highest activity (polymerization rate, active site concentration and polymer yield) at lower content of applied titanium and greater specific surface of the catalyst.
Any heterogeneous catalytic system has catalyst particles definitely distributed in it with respect to the dispersion degree. It is common knowledge that reactivity depends on the substanc,;: dispersion . Dispersion variation may induce phase or chemical equilibrium shift. 1) IS pressure. 3) where a is the surface tension; r is the particle radius. Therefore, for particles possessing spherical curvature of the surfitce, we get: _ 2cYVmol dGd -+ - - - . 4) Active sites ofpolymerization. Multiplicity 21 These equations indicate that reactivity increment stipulated by a change in dispersion is proportionate to the surface curvature ( ~ or dispersion.